31、 回答31-45题:
DNA testing DNA testing reveals the genes of each individual person. Since the early twentieth century scientists have known that all human characteristics are contained in a persons genes and are passed from parents to children. Genes work as a chemical instruction manual for each part and each function of the body. Their basic chemical element is called DNA, a copy of which can be found in every cell. The existence of genes and the chemical structure of DNA were understood by the mid-1900s, but scientists have only recently been able to identify a person from just a drop of blood or a single hair.One of the most important uses of DNA testing is in criminal investigation. The very first use of DNA testing in a criminal case was in 1985 in Great Britain, when a man confessed to killing a young woman in the English countryside. Because police had found samples of the killers DNA at the scene
of the crime, a biologist suggested that it might be possible to compare that DNA to some from the confessors blood. To everyones surprise, the tests showed that he was not the killer. Nor was he guilty of a similar murder that had happened some time earlier. At that point he admitted that be had confessed to the crimes out of fear and police pressure. The police then asked 5, 000 local men for samples of their blood, and DNA testing revealed that one of them was the real murderer, so the first man was set free.
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